Issue with bwlimit after resuming a partial transfer due to a communication break

Paul Slootman paul+rsync at
Fri Jan 21 06:15:51 MST 2011

On Fri 21 Jan 2011, Alistair Dsouza wrote:
> I have set the bwlimit to 10 i.e. 10 KBps. When I try to sync files the
> bwlimit is as what is
> set. I have enabled storage of partial files. When a communication break
> causes rsync to
> time out during a transfer the partial file is stored in the partial
> directory. I then try rsync
> again when the link is up. At this point I see that the bwlimit of 10KBps is
> not followed.
> rsync transfers the data as fast as possible.

How did you measure this data rate?
Are you using the --progress output? Then you need to realize that what
is shown there is not the data rate over the network, but the effective
rate at which the file is transferred. As the first part of the file is
in the partial directory, the data that needs to be transmitted is not
much more than the block checksums plus a little overhead. So then it
looks like the file is being transmitted a lot faster.

The same thing can be seen when using -z while transferring a highly
compressable file: --progress will show a much higher transfer rate than
what you've configured with --bwlimit.

This phenomenon can be easily verified by doing it over a dialup line,
or other medium that physically can't go faster than a given rate:
--progress will show higher rates than would be possible.


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